The present invention is directed to a non-contact linear position sensor for motion control applications.
In order to meet the current stringent reliability and meantime before failure (MTBF) requirements demanded by the automotive, industrial and aerospace industries, position sensors must be based on a non-contact design approach. For automotive use, the design must be suited for low cost, high volume, and high reliability. The above parent application discloses and claims an angular position sensor which is useful, for example, in the automotive field for determining the rotation of a steering column. This same type of non-contacting position sensor can also be adapted to measure the torque in a steering column as disclosed in a co-pending application, Ser. No. 09/527,088 (now U.S. Pat. No. 6,304,076), filed Mar. 16, 2000, entitled, NON-CONTACTING TORQUE SENSOR and assigned to the present Assignee. However, there is still a need for a linear position sensor, for example, one that may be used with a voice-coil actuator in order to provide built-in feedback control for motion control applications.
It is therefore a general object of the present invention to provide a non-contact linear position sensor for motion control applications.
In accordance with the above object there is provided a position sensor for sensing rectilinear movement of an object along an axis comprising a pair of spaced substantially rectilinear radio transmit and receive sections juxtaposed on the axis facing each other with a coupler section between them, the coupler being movable along the axis and connected to the object. The receive section carries a predetermined number of independent inductive coils segmentally arranged in a rectilinear pattern along the receive section. The transmit section carries coil means in a rectilinear pattern similar to the receive section and is driven by a signal source at a predetermined radio frequency for inductive coupling to the coils of the receive section. The coupler section carries at least one symmetrical conductive pattern for attenuating the inductive coupling, the pattern having linear positions of maximum and minimum attenuation with respect to any one of a plurality of inductive coils carried by the receive section, intermediate positions of the pattern between the maximum and minimum providing substantially proportionate attenuations. Means connected to the coils carried by the receive section demodulate and sum induced transmitted signals from the signal source for each linear position of the coupler, the summation producing a substantially sinusoidal waveform whose phase shift varies in proportion to the linear movement coupler section. Means are provided for sensing the phase shift.